Background: ALK tyrosine kinase inhibitors (TKI) have revolutionized the treatment of ALK+ non-small cell lung cancer (NSCLC), and therapy resistance occurs in virtually all patients. Multiple TKI resistance mechanisms have been characterized, including ERBB receptor coactivation. In this study, we investigated the role of HER3 in ALK TKI resistance.
Methods: In vitro studies were carried out using ALK+ NSCLC cell lines H3122, H2228, and DFCI032. Pharmacological co-targeting of ALK and HER3 was investigated with ALK and ERBB TKIs, and HER3 knockdown was achieved using the CRISPR-Cas9 system. Co-localization of ALK and HER3 was investigated by immunoprecipitation (IP) and proximity ligation assay (PLA) in vitro and in vivo using six ALK+ NSCLC tumor samples.
Results: In all tested cell lines, combined targeting with ALK and pan-ERBB TKI resulted in marked inhibition of colony formation and long-term (72 h) downregulation of pAKT levels. HER3 knockdown resulted in multiple effects on ALK+ cell lines, including the downregulation of ALK expression and visible morphological changes (H2228). Co-immunoprecipitation (IP) and proximation ligation assay (PLA) experiments provided evidence that both ALK and HER3 could interact in vitro, and this finding was verified by PLA using ALK+ NSCLC tumors.
Conclusions: This study provides evidence that HER3 may mediate TKI resistance in ALK+ NSCLC. Interestingly, we were able to show that both translocated ALK and HER3 could interact. Joint targeting of ALK and HER3 could be further investigate in ALK+ NSCLC.
Keywords: ALK; HER3; NSCLC; interaction; treatment resistance.